Experimental Study On Crack Widths Of Reinforced Concrete Beams With Stainless Steel Bars

The use of stainless steel reinforcement in the concrete structure in special environment can greatly reduce the maintenance cost of the structure in the service life,extend the service life of the structure and better solve the durability problem of the concrete structure.In recent years,many projects at home and abroad,especially harbour structure,bridge structure and island structure,have been equipped with stainless steel bars to improve the durability of structures.At present,the research on stainless steel reinforced concrete structure mainly focuses on the structure with foreign stainless steel reinforcement,while the research on the structure with domestic stainless steel reinforcement is very few.Since the elastic modulus of domestic stainless steel bars is obviously lower than that of ordinary steel bars,the crack width and deflection of domestic stainless steel reinforced concrete members must be different from that of ordinary reinforced concrete members under the same condition.Therefore,it is necessary to study the crack width and deflection of domestic stainless steel reinforced concrete members,and analyze the influence of the reduction of elastic modulus on the crack width and deflection,as well as whether the crack width calculation formula of China's code is applicable to domestic stainless steel reinforced concrete members.In this paper,crack width and deflection measurements were carried out on 11 domestic stainless steel reinforced concrete beams.The short-term crack width,short-term deflection and bending capacity of the test beam under normal service load were obtained;By comparing the test beam with the HRB series reinforced concrete beam,the influence of the elastic modulus reduction on the crack width is analyzed;Through the comparison among the test beams,the influence of reinforcement ratio and concrete strength on the crack width of domestic stainless steel reinforced concrete beams is analyzed;The short-term crack width,short-term deflection and flexural capacity of test beams under normal service load are compared with the calculated values of the code,and the applicability of the code formula to domestic stainless steel reinforced concrete beams is studied.The following conclusions are drawn from the experimental study:(1)The domestic stainless steel bar used in this test is 500 MPa grade strength steel bar.There is no obvious yield platform for the steel bar,the strength-yield ratio andthe maximum elongation ratio are large.However,the elastic modulus of the stainless steel bars is relatively small,and the elastic modulus of steel bars with different diameters is different,which varies from 110 to 170 GPa.(2)Because the elastic modulus of stainless steel bars is small,the crack width of stainless steel reinforced concrete beams is larger than that of HRB500 MPa reinforced concrete beams with the same section size and reinforcement.Besides,the crack width of stainless steel reinforced concrete beams under normal service load is slightly larger than the crack width limit specified in the code.(3)Under the normal service conditions,the average crack width formula adopted in the code is applicable to stainless steel reinforced concrete beams.The measured average crack width is in good agreement with the calculated average crack width.The short-term maximum crack width enlargement coefficient obtained by statistical analysis of the test data is less than the value in the code,but considering that the test data is less and is beneficial to the structure,the short-term maximum crack width enlargement coefficient of stainless steel reinforced concrete flexural members should still adopt the value in the code.(4)Under the normal service conditions,the short-term deflection calculation formula adopted by the code is applicable to stainless steel reinforced concrete beams,and the measured short-term deflection is in good agreement with the calculated deflection.The test data shows that the deflection of the stainless steel reinforced concrete beams under the normal use load meets the specified deflection limit requirements.(5)The calculation formula of the flexural bearing capacity adopted by the code is applicable to stainless steel reinforced concrete beams.Since the stainless steel bar has no yielding platform and the strength is relatively large,the flexural bearing capacity calculated by the canonical formula has a certain safety reserve.The innovation points of this article:(1)Through the analysis of experimental data,the effects of elastic modulus,reinforcement ratio and concrete strength on the crack widths of concrete beams are obtained.(2)Through crack test,it can be analyzed whether the short-term crack width,short-term deflection and bearing capacity of domestic stainless steel reinforced concrete beams are in agreement with the calculated values of the standard formula.It is also analyzed whether the crack width and deflection of the test beams meet thespecification limit.